1. Field of the Invention
The present invention relates generally to the field of optical switching. More specifically, the present invention relates to micro electro mechanical systems (MEMS) technology scanning mirrors for optical cross-connects and switches.
2. Discussion of the Related Art
Optical switching plays an important role in telecommunication networks, optical instrumentation, and optical signal processing systems. Optical switches can be used to turn the light output of an optical fiber on or off, or, alternatively, to redirect the light to various different fibers, all under electronic control.
Optical switches that provide switchable cross connects between an array of input fibers and an array of output fibers are often referred to as xe2x80x9coptical cross-connectsxe2x80x9d. Optical cross-connects are a fundamental building block in the development of an all-optical communications network. Specifically, in a fiber-optic communications network that uses electronic cross-connects, data travels through many fiber-optic segments which are linked together using the electronic cross-connects. Information is converted from light into an electronic signal, routed to the next circuit pathway, then converted back into light as it travels to the next network destination. In an all-optical communications network, on the other hand, the electronic cross-connects are replaced with optical cross-connects, which eliminates the need to convert the signals between light and electronic form. Instead, information travels through the entire network in the form of light, which significantly increases the network""s ability to handle higher transmission speeds, reduces power dissipation, increases reliability, and reduces cost because the cost of the electrical devices are eliminated.
There are many different types of optical switches. In terms of the switching mechanism, optical switches have been previously categorized as belonging to one of two general classes. The first general class of optical switches employs a change of refractive index to perform optical switching and can be referred to as xe2x80x9cintegrated optical switchesxe2x80x9d or xe2x80x9celectro-optic switches.xe2x80x9d The refractive index change can be induced by electro-optic, thermal-optic, acousto-optic, or free-carrier effects. The second general class of optical switches may be referred to as xe2x80x9cbulk optomechanical switchesxe2x80x9d or simply xe2x80x9coptomechanical switches.xe2x80x9d Such switches employ physical motion of one, or more, optical elements to perform optical switching. Specifically, an input fiber, typically engaged to a lens, is physically translatable from a first position to at least a second position. In each position, the input fiber optically connects with a different output fiber. In this way, a spatial displacement of a reflected beam is affected.
Optomechanical switches offer many advantages over electro-optic switches. Optomechanical switches have both lower insertion loss and lower crosstalk compared to electro-optic switches. Further, optomechanical switches have a high isolation between their ON and OFF states. Furthermore, optomechanical switches are bidirectional, and are independent of optical wavelength, polarization, and data modulation format. An optomechanical switch can be implemented either in a free-space approach or in a waveguide (e.g., optical fiber) approach. The free-space approach is more scalable, and offers lower coupling loss compared to the waveguide approach.
A number of different micromachining technologies have been developing. Recently, a micromachining technology known has micro electro mechanical systems (MEMS) technology has been shown to offer many advantages for building optomechanical switches. MEMS technology is technology characteristic of sizes from a few millimeters to hundreds of micrometers. MEMS technology is similar to semiconductor electronics fabrication except that the resulting devices possess mechanical functionality, as well as electronic and/or optical functionality. MEMS technology is currently used to fabricate movable microstructures and microactuators. MEMS can significantly reduce the size, weight and cost of optomechanical switches. The switching time can also be reduced because of the lower mass of the smaller optomechanical switches.
Many MEMS optomechanical switches and cross-connects employ movable micromirrors. MEMS movable micromirror assemblies may be used for optical scanning. That is, MEMS mirror assemblies may be used to rapidly traverse a range of positions in a coordinate axis. Thus, MEMS mirror assemblies may be used as a basic building block for optical scanners. Optical scanners are ideal for use in optical cross-connects. Optical scanners function by changing the angle of the optical beam with respect to the information medium. Various different types of scanners are capable of operating in one dimension (1D), two dimensions (2D), or even three dimensions (3D).
A 2D optical cross-connect (or switch) can be constructed by using MEMS micromirrors that move in only 1D. For example, by using vertical micromirrors, where the mirror surface is perpendicular to the substrate, a simple cross-connect (or matrix switch) with a regular planar array of switching cells can be realized. The input and output fibers are arranged in the same plane as the matrix substrate. When a switching or cross-connect operation is performed, the optical beam is redirected by one or more of the vertical micromirrors, but the optical beam does not leave the common plane of the input and output fibers. Thus, the vertical micromirrors move in 1D and are used to perform optical cross-connections in 2D.
A disadvantage of 2D optical cross-connects (or switches) is that they are limited in the number of input and output fibers that they can support since those fibers are arranged in the same plane as the matrix substrate. In today""s rapidly expanding communications systems there is a strong demand for higher capacity optical switches. Thus, there is a need for optical cross-connects and switches that can support a greater number of input and output fibers and that have the ability to cross-connect any of the input fibers with any of the output fibers.
The present invention advantageously addresses the needs above as well as other needs by providing a method of detecting alignment of an optical path through an optical switch. The method includes the steps of: directing a first monitor beam in a forward direction along at least a portion of the optical path, the at least a portion of the optical path including reflection off of a first moveable optical redirecting device and a second moveable optical redirecting device; detecting a position of the first monitor beam that is reflected off of the second moveable optical redirecting device; directing a second monitor beam in a reverse direction along the at least a portion of the optical path; and detecting a position of the second monitor beam that is reflected off of the first moveable optical redirecting device.
The present invention also provides a method of switching an optical input channel to an optical output channel. The method includes the steps of: directing a light beam that originates from the optical input channel toward a first moveable optical redirecting device; reflecting the light beam off of the first moveable optical redirecting device and onto a second moveable optical redirecting device; reflecting the light beam off of the second moveable optical redirecting device; directing the light beam reflected off of the second moveable optical redirecting device into the optical output channel; and directing a first monitor beam along at least a portion of a same path traveled by the light beam.
The present invention also provides a method of switching an optical input channel to an optical output channel that includes the steps of: directing a light beam received from the optical input channel toward a first wavelength selective optical redirecting device; reflecting the light beam off of the first wavelength selective optical redirecting device and onto a first moveable optical redirecting device; adjusting the first moveable optical redirecting device so that the light beam reflects therefrom and impinges upon a second moveable optical redirecting device; adjusting the second moveable optical redirecting device so that the light beam reflects therefrom and impinges upon a second wavelength selective optical redirecting device; and reflecting the light beam off of the second wavelength selective optical redirecting device and into the optical output channel.
The present invention also provides an apparatus for use in optical switching. The apparatus includes a first switch module and a second switch module. The first switch module includes an optical input channel, a first moveable optical redirecting device, and a first wavelength selective optical redirecting device positioned to reflect a light beam received from the optical input channel onto the first moveable optical redirecting device. The second switch module includes an optical output channel, a second moveable optical redirecting device, and a second wavelength selective optical redirecting device positioned to reflect the light beam received from the second moveable optical redirecting device into the optical output channel. The first switch module and the second switch module are positioned so that the light beam can be reflected from the first moveable optical redirecting device and impinge upon the second moveable optical redirecting device.
The present invention also provides an apparatus for use in optical switching that includes a first switch module. The first switch module includes an optical input channel, a first moveable optical redirecting device, and a first wavelength selective optical redirecting device positioned to reflect a light beam received from the optical input channel onto the first moveable optical redirecting device. A detector is configured to detect a position of a first monitor beam that is reflected off of the first moveable optical redirecting device and that at least a portion of which is transmitted through the first wavelength selective optical redirecting device.